Glossary Links

B

B-Myb

A protein transcription factor and a member of the A-Myb, B-Myb (MybL2) and C-Myb family found in all proliferating cells. B-Myb is the only member of this Myb family specific to embryonic stem cells and is required for both cycle progression and mitotic spindle formation. In mice, lack of the gene leads to early embryonic death, after implantation due to defects on the inner cell mass.

Babinski reflex

(Babinski sign, plantar reflex) Clinical term describing a primitive reflex, an involuntary response (reflex) that is present at birth and that normally disappears between 12 to 24 months. The reflex occurs when the sole of the foot has been firmly stroked the big toe moves toward the top of the foot and the other toes fan out. It is present in the newborn as the myelination of the corticospinal tracts has not yet been completed. Postnatal persistence (beyond 24 months or 2 years) occurs in infants with damage to the corticospinal tract.

bacteria

(bacterium, Greek, bakterion = little rod) A unicellular prokaryote cell, which exist in many different genetic and structural forms in many environments including commisural bacteria in the gastrointestinal tract and are also the cellular cause of infection.

bacterial spore

(bacterium, Greek, bakterion = little rod) An inactive and hardy form of bacteria, similar in function to a fungal spore that can survive in a metabolically dormant state for many years and can also withstand high temperatures, radiation, and toxic chemicals.

bacterial vaginosis

(BV, vaginitis) Clinical condition associated with loss of vaginal lactobacilli such as Lactobacillus acidophilus, Lactobacillus crispatus and Lactobacillus jensenii, and acquisition of complex communities of anaerobic bacteria such as species of Streptococcus. A common condition, USA about 29% of reproductive age women. Can result in an increased risk for pre-term birth, HIV-1 acquisition and pelvic inflammatory disease.

bacteriophage

Balbiani body

(mitochondrial cloud) collection of cell organelles (mitochondria, endoplasmic reticulum, and granulofibrillar material) asymmetrically located beside the nucleus in very young oocytes in some species. Appears similar to germinal granule precursors seen some species that contain a definitive germ plasm (flies, worms, and frogs). Dynamic region involved in early cell polarity and RNA localisation in the oocyte. Named after Edouard-Gérard Balbiani (1823 – 1899) a French biologist who was among the first to describe them.

Ballottement

(French, ballottement = "a tossing about") Clinical palpatory test (clinical week 6 - 20) used to detect pregnancy, when the lower uterine segment (or cervix) is tapped by examiner's finger, the fetus floats upward, then sinks again and can be felt on the finger. Not considered diagnostic as it can also be elicited in the presence ovarian cysts.

Barker Hypothesis

(Developmental Origins of Health and Disease, DOHaD, Fetal Origins Hypothesis) Term named after the researcher, Barker who began a statistical analysis in the UK, of low birth weight data (early 1900's). The hypothesis has since been renamed as the Fetal Origins Hypothesis and proposes that in utero influences can lead too permanent changes in embryo/fetus, low birth weight, which predisposes to chronic disease in adult life.

Barlow test

(Barlow maneuver) A clinical term to describe a physical examination of the newborn for developmental dysplasia of the hip (DDH). The examiner adducts the hip (bringing the thigh towards the midline) while applying light pressure on the knee, directing the force posteriorly. A positive sign is the hip being dislocatable, if the hip can be popped out of socket with this test. This test is then combined with the Ortolani test (maneuver). The test is named after Thomas Barlow (1845 – 1945) a British royal physician.

Barr body

Name given to a visible cellular feature at the periphery of the nucleus, produced by the inactivation of a single X chromosome in females. Named after Murray Barr (1908 – 1995), a Canadian physician and medical researcher who first identified this cellular structure.

basal body

The base of an axoneme; a cylinder about 500 nm long that resembles a centriole; the microtubule organizing center of a cilium or a eukaryotic flagellum.

basal body temperature

(bbt) The temperature taken at its lowest point in the day, typically in the morning before getting out of bed. Note that body temperature changes, an increase, is used to approximately establish the time of ovulation.

basal ganglia

(basal nuclei) A central nervous system (CNS) neural structure derived embryologically from the secondary vesicle telencephalon (endbrain) and the earlier primary vesicle prosencephalon (forebrain) from the neural tube. Structurally, it connects the cerebral cortex with the thalamus and brainstem and is associated with motor control and learning.

basal plate

The early neural tube forms into two thicker lateral regions, the basal plate and alar plate, which separate the floor plate and roof plate regions. They are divided within the lateral wall of the tube by an indentation called the sulcus limitans. The basal plate forms the ventral lateral region of the developing neural tube. At the level of the spinal cord, this region will form the motor ventral horn region.

base pair

basket cells

Central nervous system cerebellar interneurons located in the cerebellum molecular layer. These GABAergic neurons, and stellate cells, receive an excitatory synaptic input from granule cell axons (parallel fibers) and form an inhibitory synapse with Purkinje cells. The embryonic progenitors arise from the neuroepithelium at the level of of the fourth ventricle.

basonuclin 2

(bnc2, BNC2) A vertebrate zinc finger transcription factor that has a role in the proliferation of craniofacial mesenchymal cells and therefore in head and face development. (ortholog of drosophila disco proteins)

(More? PMID 16891417)

battledore placenta

(placenta battledore, batyldoure = a beating instrument) A term describing a placenta where the umbilical cord is attached at the margin. Occurs 7- 9% in singleton pregnancies and 24-33% in twin pregnancies and may effect placental function/fetal growth. The description probably comes from the similarity to a bat or paddle.

Becker muscular dystrophy

(BMD) A muscle degenerative disorder, similar to Duchenne muscular dystrophy (DMD), but allows muscles to function better than in DMD, slower progression, make a shortened form of the mutated protein. Named after Peter Emil Becker, a German doctor who first described this variant in the 1950s. PMID 13249581

beta-catenin

beta cell

Endocrine cells located in the pancreas (pancreatic islets, islets of Langerhans) that secrete insulin and increase glucose uptake. In development, their secretion stimulates fetal growth and the cells continue to proliferate to postnatal, in infancy most abundant. There are 4 different endocrine cell types (alpha, beta, delta, F-cells) in each pancreatic islet. Loss of these cells is associated with diabetes.

beta-thalassemia

A group of hereditary blood disorders caused by anomalies in the synthesis of the beta chains of haemoglobin, resulting in variable phenotypes from severe anemia to clinically asymptomatic individuals. Total annual incidence of symptomatic individuals is estimated at 1 in 100,000 throughout the world and 1 in 10,000 people in the European Union.

bilaminar embryo

(two layer embryo) Term used in early embryonic development to describe the inner cell mass differentiating to form an initial two layered structure (epiblast and hypoblast). In human development, this occurs during week 2. The epiblast layer will then form the majority of the embryo replacing the hypoblast during gastrulation during week 3.

bile salts

(conjugated bile alcohols and bile acids) Liver synthesized compounds derived from cholesterol that function postnatally in the small intestine to solubilize and absorb lipids, vitamins, and proteins. These compounds act as water-soluble amphipathic detergents.

Billings Method

Billings Ovulation Method

(BOM, Billings Method, Ovulation Method, rhythm method, Natural Family Planning) A self-observation method for women use to monitor their fertility. Used by women trying to either avoid pregnancy or trying to conceive. Named after John Billings and Evelyn Billings, two Australian doctors. Evelyn Billings co-authored the original book "The Billings Method" (1980) with Dr Ann Westmore, recently republished.

biopsy

A fragment of tissue removed for (clinical/pathological/medical) study under the microscope.

biotinidase

An enzyme required to free biotin from its bound form for use. Biotinidase deficiency can be detected in newborn screening and treated with daily biotin supplementation.

biparietal diameter

An ultrasound measurement of Biparietal Diameter (BPD) is used to determine fetal age and normal development (small/large/abnormal) parameters. Measured as the diameter between the 2 sides of the head, used in clinical ultrasound measurements after 13 weeks (2.4 cm) to term (9.5 cm). It is one of the four typical ultrasound assessments of fetal size and age: Biparietal Diameter (BPD), Head Circumference (HC), Abdominal Circumference (AC), and Femur Length (FL).

Bishop score

(Bishop's score) A clinical test prior to birth named after the obstetrician/gynaecologist Edward H. Bishop (1913-1995) who published a 1964 paper "Pelvic Scoring For Elective Induction". PMID 14199536

bladder

bladder exstrophy

(Greek, ekstriphein = "turn inside out") A congenital malformation with urinary bladder open to ventral wall of abdomen (between umbilicus and pubic symphysis) and may have other anomolies associated with failure of closure of abdominal wall and urinary bladder (epispadias, pubic bone anomolies).

blastema

blastocoel

(blastocoele, blastocele) A fluid-filled cavity that forms in early development within the blastocyst. Initially the dividing cells form a solid cellular mass (morula) continued cell division and compaction lead to the formation of this space or cavity. In humans, this cavity is present during the end of the first week and into the second week of development.

blastocyst

(Greek, blastos = sprout + cystos = cavity) Term used to describe the hollow cellular mass that forms in early development. The blastocyst consists of cells forming an outer trophoblast layer, an inner cell mass and a fluid-filled cavity. The blastocyst inner cell mass is the source of true embryonic stem cells capable of forming all cell types within the embryo. In humans, this stage occurs in the first and second weeks after the zygote forms a solid cellular mass (morula stage) and before implantation.

blastocyst hatching

(Greek, blastos = sprout + cystos = cavity) Term used to describe the process of blastocyst emerging from the surrounding protective zona pellucida. In human development this process occurs at the end of the first week (day 5-7) GA week 3. The location of hatching from the ZP can occur at the original spermatozoa entry site for fertilisation, and must complete before implantation can commence.

blastopore

blastula

(Greek, blastos = sprout = little sprout) A stage of an animal embryo that consists of a fluid-filled sphere of cells on the surface. In mammals, blastulation leads to the formation of the blastocyst, which should not be confused with the blastula. The blastocyst contains an inner embryoblast (inner cell mass), which is homologous to the blastula. However, it also includes the trophoblast, which goes on to form the extraembryonic tissues.

blood-brain barrier

(BBB) The barrier formed at the cellular level by endothelial cells of brain capillaries, differing in junctions, transport and glial association from those found in peripheral capillaries. Damage to this barrier can occur following injuries involving ischemia and reperfusion.

blood-testis barrier

(BTB) In the testis this barrier is formed by tight junctions, basal ectoplasmic specializations, desmosome-like junctions and gap junctions between adjacent Sertoli cells near the basement membrane of the seminiferous epithelium. Historically referred to as a "barrier" as intravenous dyes in rodents failed to ‘stain’ the seminiferous tubules in the testis as well as in the brain, the blood-brain barrier (BBB).

blueberry muffin baby

BMI

Acronym for Body Mass Index which is a measure of body composition. Used to determine adiposity, that is fat content, which has influences upon growth and health.

Bmi1

A proto-oncogene protein located in the nucleus, which is a member of the Polycomb-group gene family (required to maintain the repression of homeotic genes). Expressed in range of stem cells including hematopoietic, neural and intestinal stem cells. Human BMI-1 gene on the short arm of chromosome 10 (10p13). PMID: 18536716

BOC

Acronym for Brother of Cdon a cell surface receptor. CDON is also a acronym for Cell adhesion molecule-regulated/downregulated by oncogenes. Both Boc and Cdon are cell surface receptors (for sonic hedgehog) of the immunoglobulin (Ig)/fibronectin type III that interact with each other, are coexpressed and involved in neural and muscle development.

Bochdalek hernia

The most common form (80-85%) of the Congenital Diaphragmatic Hernia (CDH) types occurring mainly on the postero-lateral (left) side of the respiratory diaphragm. Due to the pleuroperitoneal foramen (foramen of Bochdalek) failing to developmentally close allowing visceral organs to enter the pleural cavity. The less common CDH form is the Morgagni hernia (through the foramen of Morgagni) occurring beside the xiphoid process of the sternum. CDH is a musculoskeletal defect which impacts upon respiratory development and function.

body mass index

(BMI) The most commonly used method of assessing whether a person is normal weight, underweight, overweight or obese. It is calculated by dividing the person’s weight (in kilograms) by their height (in metres) squared. For both adult men and women, underweight is a BMI below 18.5, acceptable weight is from 18.5 to less than 25, overweight is 25 and above (includes obese), and obese is 30 and over.

body-stalk

(connecting stalk) Historic term used to describe the early extra-embryonic mesoderm region connecting the embryonic disc to the chorion. Present mainly in week 3 of human development, this region will later form the placental cord region, becomes vascular, and connect the embryo to the placenta.

bone

A connective tissue forming the main structural component of the skeleton originating in the body from mesoderm, with some neural crest contribution in the head region. There are two processes of bone formation (ossification): endochondrial, replacing a pre-existing cartilage template (most of the skeleton); or intramembranous, ossification directly from a membrane (cranial vault, scapula). Adult bone gross histology is described as either trabecular bone (also called cancellous or spongy bone) or compact bone (does not have any spaces or hollows).

bone marrow

The cellular components found within the core of bones, mainly long bones, which contain the adult blood stem cell population and a range of other cell types. Generally described as either red marrow (myeloid tissue) or yellow marrow (mainly fat cells.)

bone marrow stromal cells

(BMSCs) These are pluripotental cells from bone marrow that can potentially differentiate into a range of connective tissue and muscle cell types (cardiomyocytes, rhabdomyocytes, hepatocytes, osteocytes, chondrocytes, tencoytes, adipocytes, smooth muscle cells). These cells have therefore been seen as a source of stem cells for tissue repair.

Botallo's duct

(ductus arteriosus, ligamentum arteriosum, ductus Botallo, ductus Botalli) A vascular shunt between pulmonary trunk and the aortic arch. This channel degenerates to form the ligamentum arteriosum (ligamentum Botalli). In preterm infants this channel may remain open as a patent ductus arteriosus. Named after Leonardo Botallo an Italian surgeon in Paris (1530-1600).

bouquet stage

Meiosis term used to describe in prophase the chromosome telomeres attachment to the inner nuclear envelope and form a cluster. This occurs before the onset of homologous pairing and synapsis. The name comes from the chromosomes resembling a "bouquet of flowers", observed in all organisms except worms (caenorhabditis elegans) and flies (drosophila).

bowel

(intestine) Term used to describe the midgut and hindgut portion of the gastrointestinal tract running from after the stomach to the anus. Also subdivided into the small bowel (small intestine) and the large bowel (large intestine).

Bowen-Conradi syndrome

(BCS) A human autosomal recessive genetic disorder characterized by a severe growth failure and psychomotor retardation, leading to death in early childhood. The cause is a mutation in the protein Essential for Mitotic Growth 1 (EMG1, Nep1), a nucleolar protein critical for ribosome biogenesis and pre-implantation mouse embryo development.

(More? PMID 20858271)

Bowman's capsule

Term describing the cup-shaped double epithelium surrounding the glomerulus of the nephron within the kidney. The outer parietal layer is a squamous simple epithelium. The inner visceral layer is formed by podocytes covering glomerular capillaries. Named after Sir William Bowman (1816 - 1892), an English physician and physiologist.

BPD

Brachet's cleft

A visible cleft separates mesendoderm and ectoderm that appears during early gastrulation. This region is also a fibronectin-rich extracellular matrix that generates a Chordin, secreted by the dorsal Spemann organiser, morphogen gradient.

brachial plexus

(Latin, bracchium = arm) The mixed spinal nerves innervating the upper limb form a complex meshwork (crossing). Formed by union of the anterior divisions of the lower 4 cervical nerves and the greater part of the anterior division of the first thoracic nerve.

brachiocephalic trunk

(Latin, bracchium = arm, cephalicus = head) The blood vessel forming the first branch of the aortic arch, arises superolaterally and splits into the right subclavian and the right common carotid arteries.

brain

The general term for the central nervous system (CNS) component formed initially from the cranial end of the neural tube. The remainder of the CNS is the spinal cord. The brain forms initially as 3 primary brain vesicles which later form 5 secondary brain vesicles.

branchial arch nerve

branchial arch pouch

breech

A birth term where the fetal buttocks are presented first, this can also occur in different forms depending on the fetal structure presentation (complete breech, frank breech, footing breech, knee breech).

Brenner hypothesis

A clinical renal hypothesis that states, individuals with a congenital reduction in nephron number have a much greater likelihood of developing adult hypertension and subsequent renal failure. Developed in the 1980's by Barry Brenner at the Brigham and Women's Hospital, this also fits with the [Abnormal Development - Developmental Origins of Health and Disease|DOHAD hypothesis].

bronchi

(Latin, bronchos = windpipe) Plural of bronchus, the two subdivisions of the trachea carrying air to the lungs. Embryologically forms as an endodermal outpocket of the foregut which branch (bronchiole, subdivision of the bronchus) as they grow.

bronchopulmonary dysplasia

bronchus

(Latin, bronchos = windpipe) The individual division of the trachea carrying air to the lungs. Develops as an endodermal outpocket of the foregut which branch repeatedly as they grow (bronchiole, subdivision of the bronchus).

brown adipose

(brown fat) Neonatal specialized form of adipose tissue used in mammals to generate body temperature (thermogenic organ) by non-shivering thermogenesis. Adult fat (white adipose) cannot be used in this fashion. This form of adipose tissue is also seen in animals that hibernate.

Bruce effect

brucellosis

(Malta fever, Mediterranean fever) A common bacterial zoonotic disease, the human form is transmitted mainly through unpasteurised dairy products derived from infected animals (sheep, goats, cow). Brucella species are small Gram negative coccobacilli, after infection the period of incubation can last from two to eight weeks, and during the first trimester lead to increased rates of spontaneous abortion.

(More? PMID 18162038)

buccal

(Latin, bucca = cheek) A term used to relate to the mouth (oral cavity).

buccopharyngeal membrane

(oral membrane; Latin, bucca = "cheek") A membrane which forms the external upper membrane limit (cranial end) of the early gastrointestinal tract (GIT). This membrane develops during gastrulation by ectoderm and endoderm without a middle (intervening) layer of mesoderm. The membrane lies at the floor of the ventral depression (stomadeum) where the oral cavity will open and will breakdown to form the initial "oral opening" of the gastrointestinal tract. The equivilent membrane at the lower end of the gastrointestinal tract is the cloacal membrane.

bud stage

Tooth stage development occurring after placode and before cap stage. At the sites of the dental placodes the epithelial cells proliferate and intrude within the mesenchyme forming the tooth buds. At this developmental stage the odontogenic potential is lost form the epithelium and granted to the ectomesenchyme.

bulbar ridge

Term describing a spiral region in the developing heart bulbus cordis, there is a left and right bulbar ridge, that contribute to the septation of membranous portion of ventricular septum that is continuous with the outflow tract. These regions fuse to separate the single embryonic outflow tract into the aortic and pulmonary arteries.

Glossary Comments

Use this page to access brief definitions of specific embryology terms. Additional information can be accessed from links listed at the end of each definition. Glossary from the UNSW Embryology program compiled and written by Dr Mark Hill. Reference material used in preparing this glossary list includes: texts listed on page 1 "Reading" of each notes section, Department of Anatomy Publications, WWW resources from NCBI, NIH, OMIM, NHMRC (Australia), AMA (USA), Office of Rare Diseases (USA), PubMed Medline Dictionaries, MSDS, Merck Manual home edn. and WHO ART terminology (2009).

These notes are for Educational Purposes Only Please email Dr Mark Hill if you wish to make a comment about this current project.